Objective To evaluate the prevalence of comorbidity among patients with prostate cancer in relation to tumour and patient characteristics and to assess if comorbidity was a determining factor in the treatment choice for patients with localized prostate cancer.

Patients and methods Serious comorbidity was recorded in the Eindhoven Cancer Registry (according to a published list of such diseases) for all patients (2941) with prostate cancer newly diagnosed between 1993 and 1996 in the southern part of The Netherlands.

Logistic regression was then used to assess which factors determined the treatment choice.

Results The prevalence of at least one serious comorbid condition was 38% for patients aged 60-69 years, 48% when aged 70-74 years and 53% for those aged >= 75 years, the cardiovascular and chronic obstructive lung diseases being most frequent.

Patients aged 60-69 years were more likely to be treated with radical prostatectomy for moderately differentiated tumour confined to the prostate, or when younger and diagnosed in a hospital with a high case-load.

The presence of comorbidity had little influence of this choice.

Conclusion Comorbidity was common in patients with prostate cancer, but the decision of urologists in the southern Netherlands to use radical prostatectomy was determined largely by the patient's age and the urologist's experience.